In Australian patent 546327, a detector mounted externally of the vehicle continuously monitors rain to provide a value for the amount of rain fallen since the completion of the last wipe of the windscreen wiper blade. Once that rain total reaches some predetermined level the wiper blade is again actuated. Such is typical of prior art automatic windscreen wiper controls which integrate detected actual rainfall signals in order to determine the rate or frequency of windscreen wiper operation.
However, such systems are in general deficient, at least in regard to the fact that the windscreen needs to be wiped not only in consideration of rainfall, but also in consideration of other water sources such as spray from nearby cars.
It is known to control windscreen wiper systems in response to measurements taken by a moisture sensing device. Typically in the prior art the moisture sensing device attempts to measure the rate of precipitation and the control attempts to initiate a wiping action once some predetermined amount of precipitation has occurred. While many such systems have been postulated, very few have apparently come into existence and those generally suffer erratic operation under at least certain conditions.